Oklahoma tornadoes: Two upgraded from EF-3 to EF-4

Two of the six EF-3 rated tornadoes that touched down during Monday's tornado outbreak have been upgraded to an EF-4 rating.

Deadly tornadoes that hit the Moore-Choctaw area and the Norman-Little Axe area were given a more powerful preliminary rating today after the National Weather Service analyzed additional ground and aerial survey data.

The Moore-Choctaw tornado, which killed 55-year-old Wilbern Patterson, was rated as an EF-4 because of photographic evidence of a residential area near Interstate 40 and Choctaw near the spot where a recreational vehicle blew over on Patterson, the weather service said.

The Norman-Little Axe tornado, which resulted in the death of 29-year-old Tammy Rider, was upgraded because of damage assessments near the end of the tornado track, the weather service said.

Tornadoes are rated from 0 to 5 on the Enhanced Fujita Scale based on the damage they cause. An EF-3 twister has wind speeds of between 136 and 165 mph. An EF-4 tornado has wind speeds between 166 and 200 mph.